1. Field of the Invention
This invention relates to monitoring systems for indicating the presence or absence of hydrocarbon vapor and water vapor in subterranean locations and more particularly relates to a monitoring system for use in conjunction with underground hydrocarbon storage tanks, industrial waste sites, and the like, with the detection of the presence of a hydrocarbon being by an adsorptive gas vapor sensor and the presence of liquid water being detected by a galvanic cell, both such sensors being powered by a solar cell so that the system does not require any external power.
2. Description of the Prior Art
Combination hydrocarbon and water level sensors are broadly known. Adsistor Technology, Inc. of Seattle, Wash. has for some time manufactured and marketed such a sensor system involving an adsorption type hydrocarbon vapor sensor and a magnetic proximity switch-float assembly for water level detection, the sensor and switch-float being housed in a slotted PVC pipe, the assembly being about seven inches long and two inches in diameter. The float on encountering sufficient water rises and opens the normally closed magnetic proximity switch. The assembly is attitude sensitive, requiring that it be arranged substantially vertically in order for the float to operate and the gas sensor and associated circuitry are powered by an external 12-volt battery.
Also known is the monitoring system disclosed in Pugnale et al U.S. Pat. No. 4,561,292, which system is used for double-wall underground storage leak detection but involves a completely different approach with leak detecting liquid filling the space between the tank walls and extending to a liquid level above ground.
Maltby et al U.S. Pat. No. 4,208,909 and Larson et al U.S. Pat. No. 4,389,889 broadly involve detecting two parameters, i.e. fluid level and the presence or composition of the fluid, with the fluid level sensor including conductive electrodes. However, Larson et al differentiates between water and other liquid fuel by relative conductivity and Maltby et al measures liquid composition and liquid level with composition measuring circuitry being utilized to provide a compensated or actual liquid level indication.
Harper U.S. Pat. No. 3,678,749, Kankura et al U.S. Pat. No. 4,188,826, Hinshaw et al U.S. Pat. No. 4,279,078 and Tokard U.S. Pat. No. 4,377,550 all disclosed galvanic type liquid level detectors.